1. Importing candy data

candy_file <- "candy-data.txt"

candy = read.csv(candy_file, row.names=1)
head(candy)

Q1. How many different candy types are in this dataset?

nrow(candy)
## [1] 85

Q2. How many fruity candy types are in the dataset?

sum(candy$fruity)
## [1] 38

2. What is your favorate candy?

candy["Twix", ]$winpercent
## [1] 81.64291

Q3. What is your favorite candy in the dataset and what is it’s winpercent value?

candy["Skittles original", ]$winpercent
## [1] 63.08514

Q4. What is the winpercent value for “Kit Kat”?

candy["Kit Kat", ]$winpercent
## [1] 76.7686

Q5. What is the winpercent value for “Tootsie Roll Snack Bars”?

candy["Tootsie Roll Snack Bars", ]$winpercent
## [1] 49.6535

Q6. Is there any variable/column that looks to be on a different scale to the majority of the other columns in the dataset?

#install.packages("skimr")
library("skimr")
skim(candy)
Data summary
Name candy
Number of rows 85
Number of columns 12
_______________________
Column type frequency:
numeric 12
________________________
Group variables None

Variable type: numeric

skim_variable n_missing complete_rate mean sd p0 p25 p50 p75 p100 hist
chocolate 0 1 0.44 0.50 0.00 0.00 0.00 1.00 1.00 ▇▁▁▁▆
fruity 0 1 0.45 0.50 0.00 0.00 0.00 1.00 1.00 ▇▁▁▁▆
caramel 0 1 0.16 0.37 0.00 0.00 0.00 0.00 1.00 ▇▁▁▁▂
peanutyalmondy 0 1 0.16 0.37 0.00 0.00 0.00 0.00 1.00 ▇▁▁▁▂
nougat 0 1 0.08 0.28 0.00 0.00 0.00 0.00 1.00 ▇▁▁▁▁
crispedricewafer 0 1 0.08 0.28 0.00 0.00 0.00 0.00 1.00 ▇▁▁▁▁
hard 0 1 0.18 0.38 0.00 0.00 0.00 0.00 1.00 ▇▁▁▁▂
bar 0 1 0.25 0.43 0.00 0.00 0.00 0.00 1.00 ▇▁▁▁▂
pluribus 0 1 0.52 0.50 0.00 0.00 1.00 1.00 1.00 ▇▁▁▁▇
sugarpercent 0 1 0.48 0.28 0.01 0.22 0.47 0.73 0.99 ▇▇▇▇▆
pricepercent 0 1 0.47 0.29 0.01 0.26 0.47 0.65 0.98 ▇▇▇▇▆
winpercent 0 1 50.32 14.71 22.45 39.14 47.83 59.86 84.18 ▃▇▆▅▂

Winpercent is on a different scale to the majority of the other variables that are on a 0 to 1 scale.

Q7. What do you think a zero and one represent for the candy$chocolate column?

0 means that the candy has no chocolate in it, and 1 means that it does not.

Q8. Plot a histogram of winpercent values

hist(candy$winpercent)

Q9. Is the distribution of winpercent values symmetrical?

No

Q10. Is the center of the distribution above or below 50%?

It is below 50%.

Q11. On average is chocolate candy higher or lower ranked than fruit candy?

mean(candy$winpercent[as.logical(candy$chocolate)])>mean(candy$winpercent[as.logical(candy$fruity)])
## [1] TRUE

Chocolate candy is on average higher ranked than fruit candy.

Q12. Is this difference statistically significant?

t.test(candy$winpercent[as.logical(candy$chocolate)], candy$winpercent[as.logical(candy$fruity)])
## 
##  Welch Two Sample t-test
## 
## data:  candy$winpercent[as.logical(candy$chocolate)] and candy$winpercent[as.logical(candy$fruity)]
## t = 6.2582, df = 68.882, p-value = 2.871e-08
## alternative hypothesis: true difference in means is not equal to 0
## 95 percent confidence interval:
##  11.44563 22.15795
## sample estimates:
## mean of x mean of y 
##  60.92153  44.11974

Yes, the difference is statistically significant.

3. Overall Candy Rankings

Q13. What are the five least liked candy types in this set?

head(candy[order(candy$winpercent),], n=5)

Q14. What are the top 5 all time favorite candy types out of this set?

tail(candy[order(candy$winpercent),], n=5)

Q15. Make a first barplot of candy ranking based on winpercent values.

library(ggplot2)

ggplot(candy) + 
  aes(winpercent, rownames(candy)) +
  geom_col()

Q16. This is quite ugly, use the reorder() function to get the bars sorted by winpercent?

ggplot(candy) + 
  aes(winpercent, reorder(rownames(candy),winpercent)) +
  geom_col()

my_cols=rep("black", nrow(candy))
my_cols[as.logical(candy$chocolate)] = "chocolate"
my_cols[as.logical(candy$bar)] = "brown"
my_cols[as.logical(candy$fruity)] = "pink"
ggplot(candy) + 
  aes(winpercent, reorder(rownames(candy),winpercent)) +
  geom_col(fill=my_cols)

Now, for the first time, using this plot we can answer questions like:

Q17. What is the worst ranked chocolate candy?

It is Charlseton Chew.

Q18. What is the best ranked fruity candy?

It is Starburst.

4. Taking a look at pricepercent

#install.packages("ggrepel")
library(ggrepel)

# How about a plot of price vs win
ggplot(candy) +
  aes(winpercent, pricepercent, label=rownames(candy)) +
  geom_point(col=my_cols) + 
  geom_text_repel(col=my_cols, size=3.3, max.overlaps = 5)
## Warning: ggrepel: 53 unlabeled data points (too many overlaps). Consider
## increasing max.overlaps

Q19. Which candy type is the highest ranked in terms of winpercent for the least money - i.e. offers the most bang for your buck?

It is Reeses Miniatures.

Q20. What are the top 5 most expensive candy types in the dataset and of these which is the least popular?

ord <- order(candy$pricepercent, decreasing = TRUE)
head(candy[ord,c(11,12)], n=5)

Nik L Nip is the least popular among the top 5 most expensive candy types in the dataset.

5. Exploring the correlation structure

#install.packages("corrplot")
library(corrplot)
## corrplot 0.92 loaded
cij <- cor(candy)
corrplot(cij)

Q22. Examining this plot what two variables are anti-correlated (i.e. have minus values)?

Fruity and chocolate

Q23. Similarly, what two variables are most positively correlated?

Winpercent and chocolate

6. Principal Component Analysis

pca <- prcomp(candy, scale=TRUE)
summary(pca)
## Importance of components:
##                           PC1    PC2    PC3     PC4    PC5     PC6     PC7
## Standard deviation     2.0788 1.1378 1.1092 1.07533 0.9518 0.81923 0.81530
## Proportion of Variance 0.3601 0.1079 0.1025 0.09636 0.0755 0.05593 0.05539
## Cumulative Proportion  0.3601 0.4680 0.5705 0.66688 0.7424 0.79830 0.85369
##                            PC8     PC9    PC10    PC11    PC12
## Standard deviation     0.74530 0.67824 0.62349 0.43974 0.39760
## Proportion of Variance 0.04629 0.03833 0.03239 0.01611 0.01317
## Cumulative Proportion  0.89998 0.93832 0.97071 0.98683 1.00000
plot(pca$x[,1:2])

plot(pca$x[,1:2], col=my_cols, pch=16)

# Make a new data-frame with our PCA results and candy data
my_data <- cbind(candy, pca$x[,1:3])
p <- ggplot(my_data) + 
        aes(x=PC1, y=PC2, size=winpercent/100, text=rownames(my_data), label=rownames(my_data)) +
        geom_point(col=my_cols)

p

library(ggrepel)

p + geom_text_repel(size=3.3, col=my_cols, max.overlaps = 7)  + 
  theme(legend.position = "none") +
  labs(title="Halloween Candy PCA Space", subtitle="Colored by type: chocolate bar (dark brown), chocolate other (light brown), fruity (red), other (black)", caption="Data from 538")
## Warning: ggrepel: 41 unlabeled data points (too many overlaps). Consider
## increasing max.overlaps

library(plotly)
## 
## Attaching package: 'plotly'
## The following object is masked from 'package:ggplot2':
## 
##     last_plot
## The following object is masked from 'package:stats':
## 
##     filter
## The following object is masked from 'package:graphics':
## 
##     layout
ggplotly(p)
par(mar=c(8,4,2,2))
barplot(pca$rotation[,1], las=2, ylab="PC1 Contribution")

Q24. What original variables are picked up strongly by PC1 in the positive direction? Do these make sense to you?

Fruity, hard, and pluribus are picked up strongly by PC1 in the positive direction. It makes sense to me since they are positively correlated each other.